Page 209 - Gear Technology Solutions

14.4 Finding the Pressure Angle of an Existing Spline

If the splines are being designed, then one of the preferred pressure angles
from the standards should be used. ANSI and DIN offer the choice between
30°, 37.5° and 45°. In the JIS standard also a pressure angle of 20° is pro-
posed.

Figure 8: Measurement of topland root and depth

If the spline is designed for an aftermarket product (for example the sprocket
shown in Figure 7), then a simple measurement, preferably on a CMM or with
a Vernier caliper as shown in Figure 8 can be conducted to obtain a first pres-
sure angle estimation. If the aftermarket product is the sprocket (not the shaft),
then it would be desirable to obtain the measurement explained in Figure 8 on
the spline shaft.

The measurement results are used together with the depth of the spline tooth
to calculate the approximated pressure angle:

a approx = arctan[(t1-t2)/2)/Depth]

In case of a topland t2 = 2.60mm, a root width t1 = 7.30 and a Depth of 2.0mm
the approximated pressure angle is:

a approx = arctan[(7.30–2.60)/2)/2.0] = 49.60°

The approximated angle is between the preferred angle 37.5° and 45° from the
standards. The difference to 45° is 4.61° and the difference to 37.5° is only
2.89°. The decision therefore is 37.5°:

a External = a Internal = 45°

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